Systems and methods for counter flow management and valve motion sequencing in enhanced engine braking

ABSTRACT

Systems and methods for managing excessive intake flow path pressure and counter flow are implemented to support enhanced engine braking applications, such as 2-stroke or 1.5-stroke engine braking implementations where the intake flow path may be exposed to excessive transient pressures in the combustion chamber during activation or deactivation of an engine brake. Intake throttle, exhaust gas recirculation (EGR) valve, intake manifold blow-off valve, compressor bypass valve, exhaust throttle, turbocharger geometry or turbocharger waste gate may be controlled to effectuate counter flow management separately or in combination. Excessive transient conditions may also be prevented or managed by sequential valve motion in which brake motion activation occurs first and then exhaust valve main event deactivation occurs second. Delay between brake activation and main event deactivation may be facilitated using mechanical and/or hydraulic implements as well as electronically.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Patent Application Ser. No.62/540,763, filed on Aug. 3, 2017, titled “METHOD FOR CONTROLLING INTAKECOUNTER FLOW SEEN DURING HPD TRANSIENT,” the disclosure and teachings ofwhich are incorporated in their entirety herein by this reference.

FIELD

This disclosure relates generally to systems and methods for operatinginternal combustion engines and for implementing engine braking actionsin internal combustion engines. More particularly, this disclosurerelates to systems and methods for managing intake flow path counterflow in enhanced braking systems. This disclosure also relates tosystems and methods for controlling valve motion in enhanced enginebraking systems.

BACKGROUND

Internal combustion engines typically employ mechanical, electrical orhydro-mechanical valve actuation systems to control the flow ofcombustible components, typically fuel and air, to one or morecombustion chambers during operation. Such systems control the motionand timing of intake and exhaust valves during engine operation and mayinclude a combination of camshafts, cam followers, rocker arms, pushrods and other elements (such elements, in combination, constituting avalve train), which are driven by a rotating engine crankshaft. Thetiming of valve actuation may be fixed by the size and location of thelobes on the camshaft.

During positive power operation, for each full 360-degree rotation ofthe camshaft, the engine sequentially completes an intake stroke,compression stroke, power or expansion stroke and then an exhauststroke. During the intake stroke, intake valves are opened to admit fueland air into a cylinder for combustion. During the compression stroke,both exhaust and intake valves are closed to permit compression by apiston of the air fuel mixture in the combustion chamber. The exhaustand intake valves remain closed as the compressed air/fuel mixtureexplodes forcing the piston downward in the expansion or power stroke.During the exhaust stroke, exhaust valves are subsequently opened toallow combustion products to escape the cylinder. Valve motion duringthis four-stroke operation is typically referred to as “main event”operation of the valves.

In addition to positive power main event operation, valve actuationsystems may be configured to facilitate “auxiliary events” duringauxiliary engine operation. For example, it may be desirable to actuate(lift) the exhaust valves during a compression stroke forcompression-release (CR) engine braking, bleeder braking, exhaust gasrecirculation (EGR), brake gas recirculation (BGR) or other auxiliaryvalve events. Other auxiliary valve actuations applied to intake valvesare also known in the art. During these auxiliary events, valve timingand motion may be controlled in a different manner compared to the mainevent operation.

For auxiliary events, “lost motion” devices may be utilized in the valvetrain to facilitate auxiliary event valve movement. Lost motion devicesrefer to a class of technical solutions in which valve motion ismodified compared to the motion that would otherwise occur as a resultof a respective cam surface alone. Lost motion devices may includedevices whose length, rigidity or compressibility is varied andcontrolled in order to facilitate the occurrence of auxiliary events inaddition to main event operation of valves.

So-called 4-stroke compression release engine braking, which augmentsmain event valve motion by providing energy dissipation events viacontrolled exhaust valve lift during each compressionstroke—corresponding to every other instance of piston top dead center(TDC)—has long been known. More recent developments in engine brakinginclude enhanced engine braking systems, such as those marketed underthe names HIGH POWER DENSITY™ and HPD™ by Jacobs Vehicle Systems, Inc.of Bloomfield, Conn. Examples of such systems and methods are describedin U.S. Pat. No. 8,936,006, the subject matter of which is incorporatedherein in its entirety. These engine braking systems provide increasedenergy dissipation, compared to 4-stroke compression release enginebraking, by utilizing valve motions that result in energy dissipationevents corresponding to every instance of TDC. In these braking systems,a braking “2-stroke” implementation may cancel the main event motions onthe intake and exhaust valves using lost motion devices and may addsecondary or auxiliary motions to one or more of the intake and/orexhaust valves such that compression release events correspond to eachinstance of TDC. A variation of “2-stroke” braking is “1.5-stroke”braking in which the main event motion on the exhaust valve is cancelledwhile adding a secondary braking motion on one more of the exhaustvalves. In “1.5-stroke” braking, the intake valve main event motionremains unchanged. Such systems may include a “failsafe” feature inwhich low lift of the exhaust valve is provided to prevent a completelysealed condition of the cylinder.

State-of-the-art engine braking systems require more precise and complexvalve motion deactivation of such braking systems, otherwise loadsexceeding steady state may occur on the intake valve train and last forone or more engine cycles. This excessive loading may arise, forexample, when the main event exhaust motion has been “lost” or cancelledbefore a hydraulically actuated braking piston associated with anexhaust valve has been allowed sufficient time to index to its steadystate position. This may result in occurrence of the low lift “failsafe”event from the braking rocker to reduce transient intake cylinderpressure. However, such failsafe systems still cannot evacuate as muchair from the cylinder as a main event exhaust lift can. As a result, theintake rocker may open one or more valves against higher than normalcylinder pressure, resulting in high load to the intake rocker and valvetrain, as well as leaving the intake manifold and flow path exposed to ahigh-pressure pulse, which may lead to undesirable consequences, such ascounter flow in the intake manifold and surge of an upstreamturbocharger in the intake flow path.

It would therefore be advantageous to provide systems and methods thataddress the aforementioned shortcoming and others in the prior art.

SUMMARY

According to one aspect, systems and methods for managing excessiveintake flow path pressure and counter flow are implemented to supportenhanced engine braking applications, such as 2-stroke engine brakingimplementations where the intake flow path may be exposed to excessivetransient pressures in the combustion chamber during activation ordeactivation of an engine brake. These systems and methods may utilizeand control one or more engine components, such as an intake throttle,exhaust gas recirculation (EGR) valve, intake manifold blow-off valve,compressor bypass valve, exhaust throttle, turbocharger geometry orturbocharger waste gate to effectuate counter flow management separatelyor in combination.

According to a further aspect, systems and methods are provided forachieving sequential valve motion in which brake motion activationoccurs first and then main event deactivation occurs second. Thissequential valve motion operates as a proactive measure to preventexcessive intake valve train forces that would otherwise result frompremature lift of an intake valve against high combustion chamberpressures or the release of intake counterflow also resulting from highcombustion chamber pressures. Such systems and methods ensure that brakemotion activation occurs sufficiently prior in time to exhaust valvemain event disablement. A brake activation operation occurs a sufficienttime (which may be predetermined or based on current engine operatingparameters) in advance of the main event deactivation to allow the brakecomponents, such as hydraulic brake actuator pistons, to reach a steadystate position before main event deactivation occurs.

According to one aspect, delay between brake activation and main eventdeactivation may be facilitated using mechanical and/or hydraulicimplements. In one example, a solenoid valve may be utilized with a flowrestriction for causing the main even deactivation delay. In anotherexample, a single port proportional valve may facilitate delay betweenpressurization of a collapsing circuit and a braking circuit. In anotherexample, a multiple-port proportional valve may facilitate the delay. Inyet another example, a hydraulic passage may be provided of suitablelength that the main event deactivation occurs only after an enginebrake mechanism (such as a brake piston) is supplied with sufficienthydraulic fluid to reach steady state operation. In another example, aflow restricting device, such as an orifice, may regulate the flow ofhydraulic fluid and cause sufficient delay in the main eventdeactivation operation to ensure that it occurs only after the enginebrake mechanism has reached steady state operation.

According to another aspect of the disclosure, the delay may beimplemented electronically in an engine control unit (ECU) that controlsbrake activation solenoids or other electromechanical actuators and mainevent disablement solenoids or other electromechanical actuator.

DESCRIPTION OF THE DRAWINGS

The above and other attendant advantages and features of the inventionwill be apparent from the following detailed description together withthe accompanying drawings, in which like reference numerals representlike elements throughout. It will be understood that the description andembodiments are intended as illustrative examples according to aspectsof the disclosure and are not intended to be limiting to the scope ofinvention, which is set forth in the claims appended hereto.

FIG. 1 is a perspective of a prior art enhanced engine brakingconfiguration that is suitable for improvements supporting counter flowmanagement and valve sequencing aspects of the disclosure.

FIG. 2 is a cross-section of a main exhaust or intake valve rocker ofthe configuration of FIG. 1 .

FIG. 3 . is a cross-section of an intake or exhaust valve engine brakerocker and brake mechanism of the configuration of FIG. 1 .

FIG. 4 . is a graph of prior art intake and exhaust valve lift as afunction of crankshaft angle for main and auxiliary (braking) valveevents.

FIG. 5 is a schematic illustration of engine, valve actuation andcontrol components in an example system that is suitable forimplementing counter flow management and sequencing aspects describedherein.

FIG. 6 is a schematic illustration of engine components and subsystemsin an example system that is suitable for implementing counter flowmanagement aspects described herein.

FIG. 7 is a process flow illustrating example methods of managing intakecounter flow and pressure according to aspects of the disclosure.

FIG. 8 is a process flow illustrating an example method of managingintake counter flow using engine braking in cylinder subsets.

FIG. 9 is a schematic block diagram of an example apparatus and systemfor sequencing valve events in an engine brake mechanism and a lostmotion device according to aspects of the disclosure.

FIG. 10 is a process flow illustrating a method for a sequencing valveevents according to aspects of the disclosure.

FIG. 11 is a schematic diagram of conventional hydraulic circuits forcontrolling flow in a brake mechanism activation circuit and a lostmotion device (main event collapsing) circuit, including collapsingcircuit and braking circuit passages in a rocker shaft, shown in crosssection.

FIG. 12 is a schematic diagram of example hydraulic components forimplementing a braking circuit with preferential supply and a main eventcollapsing circuit controlled by a solenoid valve in an apparatus andsystem for sequencing valve events according to aspects of thedisclosure.

FIG. 13 is a schematic diagram of example hydraulic components forimplementing a braking circuit and a main event collapsing circuitcontrolled by a proportional valve in an apparatus and system forsequencing valve events according to aspects of the disclosure.

FIG. 14 is a schematic diagram illustrating active and non-active flowsin the example apparatus and system of FIG. 13 in a “brake off” status.

FIGS. 15A and 15B are schematic diagrams illustrating active andnon-active flows in the example apparatus of FIG. 13 in a “brake on”status with a single-outlet proportional valve providing fluid under afirst pressure and providing fluid in a “brake on” status under a secondpressure, sufficient to activate a main event collapsing device,respectively, according to an aspect of the disclosure.

FIGS. 16A, 16B and 16C are schematic diagrams illustrating active andnon-active flows in an example apparatus and system which utilize amultiple-outlet proportional valve. FIG. 16A illustrates a “brake off”status. FIG. 16B illustrates a “brake on” status with one outlet of theproportional valve providing flow to activate a braking circuit. FIG.16C illustrates a “brake on” status with a second outlet providing flowto activate a collapsing circuit.

FIGS. 17A and 17B are cross-sections of an example engine brakingmechanism comprising a brake piston and hydraulic passages configured toindicate when the brake piston has fully indexed according to aspects ofthe disclosure.

FIG. 18 illustrates a spool valve operated under control of a solenoidvalve to sequence activation of a braking circuit and a main eventcollapsing/deactivation circuit.

FIG. 19 illustrates example curves representing valve lift, valve trainforce and cylinder pressure as a function of time for prior art systems.

FIG. 20 illustrates example curves representing valve lift, valve trainforce and cylinder pressure as a function of tie for an enhanced brakingsystem having one or more of the valve motion sequencing aspectsdescribed herein.

DETAILED DESCRIPTION

FIGS. 1-4 illustrate aspects of an example valve actuation system for anenhanced braking system, as disclosed in U.S. Pat. No. 8,936,006, whichmay be adapted and improved in accordance with aspects of thisdisclosure. Valve actuation system 10 may include a main exhaust rockerarm 20, an engine braking exhaust rocker arm 25 to provide enginebraking motion to an exhaust valve, a main intake rocker arm 40, and anengine braking intake rocker arm 30 to provide engine braking motion toan intake valve. The rocker arms 20, 25, 30 and 40 may pivot on one ormore rocker shafts 50, which include one or more passages 51 and 52 forproviding hydraulic fluid to one or more of the rocker arms.

The main exhaust rocker arm 20 may contact an exhaust valve bridge 60,which interacts with ends of exhaust valves 81 (see FIG. 2 ), and themain intake rocker arm 40 may contact an intake valve bridge 70, whichinteracts with ends of intake valve stems (not shown). The enginebraking exhaust rocker arm 25 may contact a sliding pin 65 provided inthe exhaust valve bridge 60, which permits actuation of only a singleone of the exhaust valves 81, separately from exhaust valve bridge 60,by the engine braking exhaust rocker arm 25. The engine braking intakerocker arm 30 may contact a sliding pin 75 provided in the intake valvebridge 70, which permits actuation of only a single one of the intakevalves, separately from intake valve bridge 70, by the engine brakingintake rocker arm 30. Each of the rocker arms 20, 25, 30 and 40 may beactuated by cams and may include a cam roller, for example. The mainexhaust rocker arm 20 may be driven during main event motion by a camthat includes a main exhaust bump 26, which may selectively open theexhaust valves during an exhaust stroke for an engine cylinder.Likewise, the main intake rocker arm 40 may be driven during main eventmotion by a cam which includes a main intake bump which may selectivelyopen the intake valves during an intake stroke for the engine cylinder.Hydraulic fluid may be supplied to the rocker arm 20 from a hydraulicfluid supply (not shown) under the control of a solenoid valve 120. Thehydraulic fluid may flow through passages 51, 23 formed in the rockershaft 50 to a hydraulic passage 21 formed within the rocker arm 20. Thearrangement of hydraulic passages in the rocker shaft 50 and the rockerarm 20 shown in FIG. 2 are for illustrative purposes only.

An adjusting screw assembly 90 may be disposed at an end of the rockerarm 20. The adjusting screw assembly may comprise a screw 91 extendingthrough the rocker arm 20 which may provide for lash adjustment, and athreaded nut 92 which may lock the screw 91 in place. A hydraulicpassage 93 in communication with the rocker passage 21 may be formed inthe screw 91. A swivel foot 94 may be disposed at one end of the screw91.

The exhaust valve bridge 60 may receive a collapsing or lost motiondevice or assembly including an outer plunger 102, a cap 104, an innerplunger 106, an inner plunger spring 107, an outer plunger spring 108,and one or more wedge rollers or balls 110. The outer plunger 102 mayinclude an interior bore 105 and a side opening extending through theouter plunger wall for receiving the wedge roller or ball 110. The innerplunger 106 may include one or more recesses shaped to securely receivethe one or more wedge rollers or balls 110 when the inner plunger ispushed downward. The central opening of the valve bridge 60 may alsoinclude one or more recesses for receiving the one or more wedge rollersor balls 110 in a manner that permits the rollers or balls to lock theouter plunger 102 and the exhaust valve bridge 60 together, as shown inFIG. 2 . The outer plunger spring 108 may bias the outer plunger 102upward in the central opening. The inner plunger spring 107 may bias theinner plunger 106 upward in outer plunger bore.

A main event deactivation circuit may be associated with the mainexhaust valve rocker arm 20 and the main intake rocker arm 40 toactivate the lost motion device or assembly and thereby deactivate ordisable the main event valve motion. Hydraulic fluid may be selectivelysupplied from a solenoid control valve 120, through passages 51, 21, 23and 93 to the outer plunger 102. The supply of such hydraulic fluid maydisplace the inner plunger 106 downward against the bias of the innerplunger spring 107. When the inner plunger 106 is displaced sufficientlydownward, the one or more recesses in the inner plunger may registerwith and receive the one or more wedge rollers or balls 110, which inturn may decouple or unlock the outer plunger 102 from the exhaust valvebridge body 60. As a result, during this “unlocked” state, valveactuation motion applied by the main exhaust rocker arm 20 does not movethe exhaust valve bridge 60 downward to actuate the exhaust valves.Instead, this downward motion causes the outer plunger 102 to slidedownward within the central opening of the exhaust valve bridge againstthe bias of the outer plunger spring 108.

In addition to the lost motion device or collapsing mechanism describedabove, another suitable lost motion device for incorporation into thevalve bridges 60, 70 is described in U.S. Pat. No. 9,790,824, theteachings of which are incorporated herein by this reference.

With reference to FIGS. 1 and 3 , the engine braking exhaust rocker arm25 and engine braking intake rocker arm 30 may include brakingmechanisms that incorporate collapsing or lost motion elements such asthose provided in the rocker arms illustrated in U.S. Pat. Nos.3,809,033 and 6,422,186, which are hereby incorporated by reference. Theengine braking exhaust rocker arm 25 and engine braking intake rockerarm 30 may each have a selectively extendable actuator or braking piston132 which may take up a lash space between the extendable actuatorpistons and the sliding pins 65 and 75 provided in the valve bridges 60and 70 underlying the engine braking exhaust rocker arm and enginebraking intake rocker arm, respectively.

The rocker arm 25 may include a cam follower 135 which contacts a cam136, which may have one or more bumps to provide compression release,brake gas recirculation, exhaust gas recirculation, partial bleedervalve actuation and/or other auxiliary valve actuation motions to theexhaust side engine braking rocker arm 25. When contacting the enginebraking intake rocker arm 30, the cam 140 may have one, two, or morebumps to provide one, two or more intake events to an intake valve. Theengine braking rocker arms 25 and 30 may transfer motion derived fromcams 136 to operate at least one engine valve each through respectivesliding pins 65 and 75.

The engine braking exhaust rocker arm 25 may be pivotally disposed onthe rocker shaft which includes hydraulic fluid passages 51, 52 and 23.The hydraulic passage 23 may connect the hydraulic fluid passage 51 witha port provided within the rocker arm 25. The engine braking exhaustrocker arm 25 (and engine braking intake rocker arm 30) may receivehydraulic fluid through the rocker shaft passages 51 and 23 under thecontrol of a solenoid hydraulic control valve 120. It is contemplatedthat the solenoid control valve 120 may be located on the rocker shaft50 or elsewhere.

The engine braking rocker arm 25, 30 may also include a control valve150. The control valve 150 may receive hydraulic fluid from the rockershaft passage 23 and is in communication with a fluid passageway 160that extends through the rocker arm 25 to a lost motion piston assembly165. The control valve 150 may be slidably disposed in a control valvebore and include an internal check valve which only permits hydraulicfluid flow from passage 23 to passage 160. The design and location ofthe control valve 150 may be varied without departing from the intendedscope of the present invention. For example, it is contemplated that inan alternative embodiment, the control valve 150 may be rotatedapproximately 90 degrees such that its longitudinal axis issubstantially aligned with the longitudinal axis of the rocker shaft 50.

A second end of the engine braking rocker arm 25, 30 may include a lashadjustment assembly 170, which includes a lash screw and a locking nutlocated above the lost motion piston assembly 165. The lost motionpiston assembly 165 may include an actuator piston 132 slidably disposedin a bore provided in the head of the rocker arm 25. The borecommunicates with fluid passage 160. The actuator piston 132 may bebiased upward by a spring 133 to create a lash space between theactuator piston and the sliding pin 65.

A hydraulic brake activation circuit may be implemented in associationwith the engine braking rocker arm 25, 30. Application of hydraulicfluid to the control valve 150 from the passage 23 may cause the controlvalve to index upward against the bias of the spring above it, as shownin FIG. 3 , permitting hydraulic fluid to flow to the lost motion pistonassembly 165 through passage 160. The check valve incorporated into thecontrol valve 150 prevents the backward flow of hydraulic fluid frompassage 160 to passage 23. When hydraulic fluid pressure is applied tothe actuator piston 132, it may move downward against the bias of thespring 133 and take up any lash space between the actuator piston andthe sliding pin 65. In turn, valve actuation motion imparted to theengine braking rocker arm 25 from the cam bumps may be transferred tothe sliding pin 65 and the exhaust valve below it. When hydraulicpressure is reduced in the passage 23 under the control of the solenoidcontrol valve 120, the control valve 150 may collapse into its boreunder the influence of the spring above it. Consequently, hydraulicpressure in the passage 160 and the bore may be vented past the top ofthe control valve 160 to the outside of the rocker arm 25. In turn, thespring 133 may force the actuator piston 132 upward so that the lashspace 104 is again created between the actuator piston and the slidingpin 650. In this manner, under control from the brake activationcircuit, the exhaust and intake engine braking rocker arms 25 and 30 mayselectively provide valve actuation motions to the sliding pins 65 and75, and thus, to the engine valves disposed below these sliding pins.

FIG. 4 is a graphic representation of intake and exhaust valve motionthat may be achieved by an enhanced engine braking system as describedabove. The main exhaust rocker arm 20 may be used to provide a mainexhaust event 480, and the main intake rocker arm 40 may be used toprovide a main intake event 490 during positive power operation.

During engine braking operation, according to one embodiment, the enginebraking exhaust rocker 25 may facilitate auxiliary exhaust valve motionand events to provide enhanced engine braking. These may include astandard BGR valve event 422, an increased lift BGR valve event 424, andtwo compression release valve events 420. The engine braking intakerocker 30 may also facilitate auxiliary intake valve motion and eventsto provide enhanced engine braking. These may include two intake valveevents 430 which lift the intake valve to provide additional air to thecylinder for engine braking. In this embodiment, both exhaust 480 andintake main events 490 are deactivated or lost according to the lostmotion or collapsing mechanisms described above. In accordance withthese valve events 420, 422, 424, 430, the system may provide fulltwo-cycle or “2-stroke” compression release engine braking.

With continued reference to FIG. 4 , in a first alternative, motions ofonly the exhaust valves are modified to provide engine braking. In thisalternative, no engine braking intake rocker arm is provided nor is alost motion or collapsing component provided in the intake valve bridge.Thus, a lost motion or collapsing mechanism is only provided on theexhaust valve bridge and the engine braking mechanism is provided onlyon the engine braking exhaust rocker arm. In this case, the main intakeevent 490 is not lost and no intake braking valve events 430 areprovided, whereas the exhaust main event 480 is lost, and, in theillustrated example, the four exhaust engine braking valve events 420,422, 424 are provided. In this manner, the system provides so-called“1.5-stroke” compression release engine braking. Such a system providessignificant engine braking power comparable to a 2-stroke system, butwith reduced cost due to the unmodified intake valve actuationcomponents.

FIG. 5 is a schematic block diagram including a cross-sectional view ofan engine cylinder and illustrating valve actuation apparatus and systemsuitable for implementing the improvements in counter flow managementand valve sequencing disclosed herein. An engine controller 521 may becommunicatively associated with a number of valve actuating subsystems,generally represented by 514. The intake valve 506 and exhaust valve 508may be opened and closed by these valve actuating subsystems toimplement main event and auxiliary (braking) valve motion as describedabove. These may include a positive power or main event intake valveactuating subsystem 516, an engine braking intake valve actuatingsubsystem 522, a positive power or main event exhaust valve actuatingsubsystem 518, and an engine braking exhaust valve actuating subsystem520. The positive power valve actuating subsystems and the enginebraking valve actuating subsystems may be integrated into a singlesystem in some embodiments or separate in others.

The valve actuating subsystems 514 may be controlled by a controller 521to selectively control, for example, amount and timing of the enginevalve actuations, including the controlled signaling or energization ofsolenoids or other control elements to cause main event valve actuationsand engine braking valve actuations. The controller 521 may comprise anyelectronic, mechanical, hydraulic, electrohydraulic, or other type ofcontrol device for communicating with the valve actuating subsystems 514and causing some or all of the possible intake and exhaust valveactuations to be transferred to the intake valve 506 and the exhaustvalve 508. The controller 521 may include a microprocessor andinstrumentation linked to other engine components to determine andselect the appropriate operation of the engine valves based on inputsindicative of various engine operating parameters such as engine speed,vehicle speed, oil temperature, coolant temperature, manifold (or port)temperature, manifold (or port) pressure, cylinder temperature, cylinderpressure, particulate information, other exhaust gas parameters, driverinputs (such as requests to initiate engine braking), transmissioninputs, vehicle controller inputs, engine crank angle, and various otherengine and vehicle parameters. In particular, and in accordance withembodiments described in further detail below, the controller mayactivate the engine braking exhaust valve actuating subsystem 520 andthe engine braking intake valve actuating subsystem 522 in response to arequest for engine braking.

Referring now to FIG. 6 , an internal combustion engine 600 is shownoperatively connected to a number of other engine support subsystems andcomponents that may be utilized for intake counter flow control inaccordance with aspects of the present disclosure. The internalcombustion engine 600 comprises a plurality of cylinders 602, an intakemanifold 604 and an exhaust manifold 606. FIG. 6 also schematicallyillustrates an engine braking subsystem 620, which may comprisecomponents described above relative to FIGS. 1-4 , for actuating one ormore valves to achieve engine braking according to signals provided bycontroller 521, for example, to solenoid components 120 (FIGS. 2 and 3 )for controlling main event and engine brake valve actuation. The exhaustsystem 630 may comprise an exhaust throttle or exhaust braking subsystem632 and a turbocharger 634. As known in the art, the turbocharger 634may comprise a turbine 636 operatively connected to a compressor 638 inwhich exhaust gases (illustrated by the black arrows) output by theexhaust manifold 606 rotate the turbine 636, which in turn, drives thecompressor 638. Turbocharger 634 may be a variable geometry turbocharger(VGT) permitting variation of the turbocharger geometry under control ofthe controller 521. The geometric variation may include variable vanes(i.e., sliding or rotating vanes) to direct airflow having and/orvariable nozzles having fixed vanes to direct airflow and a slidinghousing to vary airflow. Furthermore, the turbocharger 634 may comprisea wastegate (internal or external) that may be used to divert exhaustgases away from the turbine 636 and directly into the exhaust system630. The exhaust braking subsystem 632 may comprise any of a number ofcommercially available exhaust brakes. Exhaust system 630 may alsocomprise an exhaust gas recirculation (EGR) system 609 for recirculatingexhaust gases to the engine intake. An EGR valve 607 may be operativelyconnected to the controller 521 and may be modulated in response to thecontroller 521 to achieve counter flow management in accordance withaspects of the disclosure. Collectively, the exhaust manifold 606,turbocharger turbine 636, exhaust system 630 and EGR system 609 mayconstitute an exhaust flow path.

As further shown in FIG. 6 , various components may form an intakesystem, or intake flow path, that provide air to the intake manifold604. In the illustrated example, an inlet pipe 608 provides ambient airto the compressor 638 that, in turn, provides pressurized air through acompressor outlet pipe 610 to a charge air cooler 612 that cools downthe pressurized air. The output of the charge air cooler 612 routes thecooled, compressed air to an intake manifold inlet 614. As known in theart, the level of compression (or boost pressure) provided by thecompressor 638 depends upon the pressure of the exhaust gases escapingthrough the exhaust system 630. The intake flow path may furthercomprise an intake throttle 601 disposed within the intake manifoldinlet pipe 614, a blow off valve 603 in communication with the intakemanifold inlet pipe 614 and/or a compressor bypass valve 605 incommunication with the intake manifold inlet pipe 614 and the inlet pipe608.

As further shown in FIG. 6 , a controller 521 is provided andoperatively connected via the connection points referenced “A” in FIG. 6to the braking subsystem 620, the exhaust braking subsystem 632 andother engine subsystems and components, including the intake throttle601, EGR valve 607, intake manifold blow off valve 603, compressorbypass valve 605 and turbocharger 634. The circled “A” reference denotesan operative and communicative connection. The controller connectionwith the blow off valve 603 is illustrated as being optional (i.e., indashed lines) to the extent that the blow off valve 603 may be an activeblow off valve capable of being directly controlled by the controller521, or a passive blow off valve, in which case no control signals fromthe controller 521 are provided. In an embodiment, the connectionsbetween the controller 521 and noted components may be configured toconvey signals from sensing elements integrated with the components andwhich generate signals to the controller 521. In practice, though notillustrated in FIG. 6 , the connections to the various components may beto various control elements (such as, but not limited to, integrated orexternal linear or rotary actuators, hydraulic control valves, etc.)used to control the respective components responsive to signals from thecontroller 521. In this manner, the controller 521 controls operation ofthese components and sub systems.

In the illustrated embodiment, the controller 521 may comprise aprocessor or processing device 542 coupled a storage component or memory544. The memory 544, in turn, comprises stored executable instructionsand data, which may include a counter flow management module 546 and/ora valve actuation sequencing module 548. In an embodiment, the processor542 may comprise one or more of a microprocessor, microcontroller,digital signal processor, co-processor or the like or combinationsthereof capable of executing the stored instructions and operating uponthe stored data. Likewise, the memory 542 may comprise one or moredevices such as volatile or nonvolatile memory including but not limitedto random access memory (RAM) or read only memory (ROM). Processor andstorage arrangements of the types illustrated in FIG. 6 are well knownto those having ordinary skill in the art. In one embodiment, theprocessing techniques described herein are implemented as a combinationof executable instructions and data within the memory 544executed/operated upon by the processor 542. As an example, thecontroller 521 may be implemented using an engine control unit (ECU) orthe like, as known in the art.

While the controller 521 has been described as one form for implementingthe techniques described herein, those having ordinary skill in the artwill appreciate that other, functionally equivalent techniques may beemployed. For example, as known in the art, some or all of thefunctionality implemented via executable instructions may also beimplemented using firmware and/or hardware devices such as applicationspecific integrated circuits (ASICs), programmable logic arrays, statemachines, etc. Furthermore, other implementations of the controller 521may include a greater or lesser number of components than thoseillustrated. Once again, those of ordinary skill in the art willappreciate the wide number of variations that may be used is thismanner. Further still, although a single controller 521 is illustratedin FIG. 6 , it is understood that a combination of such processingdevices may be configured to operate in conjunction with, orindependently of, each other to implement the teachings of the instantdisclosure.

FIG. 7 illustrates example processing 700 in accordance with aspects ofthe instant disclosure. In particular, the processing illustrated inFIG. 7 may be implemented by the controller 521 as described above.Beginning at block 702, the controller checks for engine brakeactivation. As noted above, such a request may be provided in the formof a user input such as through activation of a switch or otheruser-selectable mechanism as known in the art. The process checks atdecision 704 if an engine brake command has been received. If not, theprocess returns to step 702. If a command is received, the processproceeds to one or more counter flow management control steps. As willbe appreciated, and as suggested by the dotted lines around these steps,the steps may be performed in combination or separately in a givencontrol process.

The various components illustrated in FIG. 6 , i.e., the intake throttle601, the EGR valve 607, the compressor bypass valve 605, blow off valve607, exhaust throttle 632 or turbocharger 634, may be considered airflowmanagement devices. Additionally, such airflow management devicestypically have steady state operation or are configured in a steadystate position during auxiliary engine operation such as engine braking.In order to manage or mitigate the effects of counter flow duringtransition from positive power to auxiliary engine operations such asengine braking, the noted airflow management devices, eitherindividually or in combination, may be controlled to assume operation orconfiguration other than that normally employed during such steady stateoperation, as described below. TABLE A below illustrates an exampleconfiguration for the various airflow management devices of FIG. 6 ,including example positions at steady state, transient and during abraking operation.

TABLE A Airflow Typical Steady Management State Positive Braking DevicePower Position Transient Position Position Intake throttle OPEN CLOSEDOPEN EGR valve OPEN or More OPEN than during Can be OPEN CLOSED positivepower or CLOSED More OPEN than Braking CBP valve CLOSED OPEN CLOSEDExhaust throttle OPEN CLOSED OPEN VGT position OPEN or More OPEN thanduring Can be OPEN CLOSED positive power or CLOSED More OPEN thanBraking Wastegate OPEN or More OPEN than during Can be OPEN CLOSEDpositive power or CLOSED More OPEN than Braking Blow Off Valve CLOSEDOPEN CLOSEDAs is apparent from TABLE A, the airflow management devices may havedifferent operating positions during steady state operation, transitionto/from steady state to braking, and braking steady state operation.

With reference one again to FIG. 7 , if an engine braking command hasbeen received, processing may continue at step 706 where the intakethrottle 601 (refer additionally to FIG. 6 ) is used to control counterflow. In this case, the intake throttle is controlled to assume aposition in which flow through the intake manifold inlet pipe 614 isrelatively restricted and therefore below a flow level typicallyemployed during steady state engine braking, i.e., the throttle is moreclosed. In this manner, any counterflow introduced into the intakemanifold is effectively reduced from propagating all the way to theturbocharger 634.

Alternatively, or additionally, processing may continue at step 708where the EGR valve 607 is used to control counter flow. In this case,the EGR valve 607 is controlled to increase communication between theexhaust flow path (the exhaust manifold 606) and the intake flow path(the intake manifold 604) as compared to the level of communicationtypically employed during steady state engine braking, i.e., the EGRvalve 607 is more open. Controlled in this manner, the EGR valve 607effectively establishes a larger volume to receive any intakecounterflow, thereby diminishing its counter flow effect on theturbocharger compressor.

Alternatively, or additionally, processing may continue at step 709where the compressor bypass valve is controlled to decrease boostpressure provided by the turbocharger to a lower level as compared toboost pressure typically encountered during steady state engine braking.In this case, the compressor bypass valve is opened more to permit thepressurized air output by the turbocharger 634 to be rerouted to intakeinlet 608. In this manner, pressure in a given cylinder is reduced priorto initiation of engine braking, thereby decreasing the charge in thecylinder that would otherwise potentially manifest as a pressure impulse(intake counterflow). The compressor bypass valve may also be used toredirect intake counterflow around the compressor to the intake inlet.

Alternatively, or additionally, processing may continue at step 710where the intake manifold blow-off valve 603 may be activated, eitherunder control of controller 521 or independently. In the case of anactively controlled blow off valve 603, the controller instructs theblow off valve to open such that any counterflow may be immediatelyvented out of the intake manifold 604. Alternatively, in the case of apassive blow off valve 603, the blow off valve is configured (prior toauxiliary operation of the engine) to open whenever pressure within theintake flow path exceeds a predetermined threshold. For example, thepredetermined threshold can be set to a level lower than a pressurelevel in the intake manifold that is known to cause unacceptablecounterflow back to the turbocharger 634. In this case, operation of theblow off valve occurs independent of the controller 512.

Alternatively, or additionally, processing may continue at step 712where the exhaust throttle 632 may be utilized to reduce the speed ofthe turbocharger and boost pressure provided by the turbocharger to alower level as compared to boost pressure typically encountered duringsteady state engine braking. In this case, the exhaust throttle 632 ismore closed to slow the turbocharger and thereby reduce boost pressureto the cylinder, which also decreases the charge in the cylinder thatwould otherwise potentially manifest as a pressure impulse (intakecounterflow).

Alternatively, or additionally, processing may continue at step 714where the controller 521 may control the turbocharger 634, including itsgeometry and/or an associated wastegate to reduce boost pressure whichmay subsequently reduce cylinder pressure and the severity of thesubsequent high-pressure pulse in the intake flow path. For example, inthe case of a variable geometry turbocharger, fully opening theturbocharger rack will reduce the speed of the turbocharger and therebyreduce the boost pressure. In addition, for turbochargers that use anactive wastegate system (either internal or external to theturbocharger), the wastegate may be opened to once again reduce speed ofthe turbocharger and thereby reduce the boost pressure, thus achievingthe same effect.

Alternatively, or additionally, processing may continue at step 716where counter flow in the intake manifold may be further controlled byinitiating braking in only a subset of the cylinders in the engine, aswill be explained in more detail with reference to FIG. 8

As will be recognized by those of ordinary skill in the art, theabove-described steps may be performed reactively in response to sensedparameters in the engine system, such as in response to a thresholdpressure being sensed in the intake manifold, or may be performedproactively, for example, prior to control steps, such as activation ofan engine braking system and/or valve actuation system that may causecounter flow and/or a pressure increase in the intake manifold. Forexample, as described above relative to FIGS. 1-4 , engine braking inthe illustrated system is accomplished by deactivating main event motionfor the exhaust valve(s) and activating braking motion for at least oneexhaust valve. In this case, the below-described mitigation techniquesare preferably performed no later than the deactivation of main eventmotions for the exhaust valve(s). In this manner, the airflow managementcomponents can be configured or operated in a manner such that they areprepared to mitigate any potential counterflow in the intake flow path.

FIG. 8 is a process flow illustrating processing 800 for an examplemethod of facilitating braking in cylinder subsets. Beginning at block802, the controller checks for engine brake activation. As noted above,such a request may be provided in the form of a user input such asthrough activation of a switch or other user-selectable mechanism asknown in the art. The process checks at decision 804 if an engine brakecommand has been received. If not, the process returns to step 802. If acommand is received, the process, under control from controller 521(FIGS. 5 and 6 ) proceeds at step 806 to initiate engine brakingoperations, as described above, in a first group of cylinders. At step808, main event motion is deactivated in the first group (one or more)of cylinders. At step 810, braking motion is activated in the exhaust,and possibly one or more of the intake valves in the first group ofcylinders. As will be recognized, this measure of braking in a subset ofthe engine cylinders results in a lower maximum volume of air and thus alower peak pressure impulse to which the intake manifold and upstreamcomponents may be exposed. At step 812, a delay of a predeterminedamount of is allowed to expire following initiation of engine brakingfor the first group of cylinders. Preferably, the predetermined periodof time is sufficiently long enough to permit any intake manifoldpressure impulse resulting from activation of engine braking for thefirst group of cylinders to dissipate. Thereafter, at step 814, enginebraking in a second group (one or more) of cylinders, which may includeat least one cylinder not included in the first group, may be initiated.Thus, at step 817 main event motion is deactivated in the second groupof cylinders and at step 816, braking motion is activated in the atleast one exhaust valve associated with the cylinders in the secondgroup. Once again, by staging the first and second groups of cylindersin this manner, lower peak pressure impulses will be realized ascompared to simultaneous initiation of engine braking in all cylinders.Additionally, though the example illustrated in FIG. 8 described twogroups of cylinders, it will be appreciated that a larger number ofgroups could be employed. For example, in an engine comprising Ncylinders, any number of groups from 2, 3 . . . N-1 or N groups ofcylinders could be used (the example of N groups corresponding to thestaged activation of engine braking for all N cylinders separately).

FIG. 9 is a schematic block diagram of an example hydraulic apparatusand system for sequencing valve events in a brake mechanism and a lostmotion device according to aspects of the disclosure. A fluid supply 900may feed an engine brake mechanism activation circuit 910 and a lostmotion or collapsing device activation circuit 920. As used herein, acircuit comprises a hydraulic circuit used to supply hydraulic fluid toa given brake mechanism or lost motion/collapsing mechanism. An enginebrake mechanism activation valve 912 may control flow to an exhaustvalve brake mechanism 914 for activation thereof. Fluid returns to thefluid supply 900 after flow thru the exhaust valve engine brakemechanism 914. A lost motion activation valve 922 may control flow to anexhaust valve lost motion device 924. Fluid returns to the fluid supply900 after flow thru the exhaust valve lost motion device 924. As will beunderstood, the functions of the valves 912 and 922 may be separatelycontrolled, for example with separately controlled solenoid valves, ormay be integrated in a single valve, such as a single solenoid valve,single port proportional valve or multiple port proportional valve, eachwith branched flow paths corresponding to the circuits 910 and 912, aswill be described.

FIG. 10 is a process flow illustrating processing 1000 in a method for asequencing valve events according to aspects of the disclosure.Beginning at block 1002, the controller checks for engine brakeactivation. The process checks at decision 1004 if an engine brakecommand has been received. If not, the process returns to step 1002. Ifan engine braking command is received at step 1004, processing continuesat step 1006 where one or more control elements, for example an enginebrake solenoid valve, are actuated under control of engine controller521 to the engine brake mechanism. In an embodiment, the engine brakemechanism will enter a transient state in which engine brake mechanismis not capable of performing engine braking, and thereafter enter asteady state in which the engine brake mechanism is ready to performengine braking. Processing continues at step 1008 where a delay isincurred prior to activation of the lost motion mechanism at step 1010.In one embodiment, the delay may be a fixed, predetermined amount oftime based on knowledge of how long it takes the engine brake mechanismto reach its steady state, as described above. In another embodiment,the delay incurred at step 1008 may be determined according to anoperating parameter of the engine. Such engine parameter may include,but are not limited to, engine speed, hydraulic fluid (oil) temperatureand/or pressure. For example, engine speed and/or oil pressure areoperating parameters that may be utilized as inputs for determining theamount of delay. Oil pressure typically increases with engine speed. Atlow engine speeds, such as 1000 rpm, the time for the brake mechanism toreach steady state may be slower than at higher engine speeds. Thus, athigher engine speeds, the system may determine a shorter delay betweenbrake activation and main event exhaust deactivation. For furtherexample, oil temperature may be another operating parameter used todetermine delay. Typically, colder oil temperature will result in higherviscosity and thus slower activation of the brake mechanism. For verycold, subzero temperatures the activation time of the brake mechanismcould be noticeably longer as compared to a system having highertemperature oil. Conversely, hotter operating temperatures will resultin more rapid operation of the brake mechanism. Thus, the system mayutilize fluid temperatures as an operating parameter on which to basedeterminations of delay. As will be recognized, temperatures of otherfluids that corelate to hydraulic fluid or oil temperature may also beused as operating parameters. For example, coolant temperature maycorelate closely with oil temperature and may thus be used as anoperating parameter for delay determination. Additionally, or as afurther alternative, as illustrated by step 1009, the delay may be basedon a determination whether the engine brake mechanism has reached steadystate deployment, such determination being determined according tofeedback provided from the engine brake mechanism. As will berecognized, this sequence will ensure that the engine brake mechanism isin a steady state, rather than a transient state, before the main eventmotion of the associated exhaust valve(s) is lost through activation ofthe lost motion/collapsing device. Various embodiments of structuresthat may be used to achieve the sequencing described relative to FIG. 10are further described below relative to FIGS. 11-18 .

FIG. 11 is a schematic diagram of conventional hydraulic circuits forcontrolling flow in a brake mechanism activation circuit and a lostmotion device (main event collapsing) circuit, including collapsingcircuit and braking circuit passages in a rocker shaft, shown in crosssection. In this case, a conventional solenoid feeds two circuits in arocker shaft. In particular, a solenoid valve 1110, having an outlet1112 and inlet 1116, which may be controlled according to signals from acontrol unit (not shown), is provided. Rocker shaft 1150 may include abraking circuit passage 1160 and a lost motion or collapsing circuitpassage 1170. A supply passage 1180 supplies fluid to the solenoid inlet1116. In this conventional supply configuration, the solenoid valve 1110provides fluid to a braking circuit and a main event collapsing circuit,without regard to sequencing of the braking and main event collapsevalve actions.

FIG. 12 is a schematic diagram of example hydraulic components forimplementing a braking circuit with preferential supply and a main eventcollapsing circuit controlled by a solenoid valve in an apparatus andsystem for sequencing valve events according to aspects of thedisclosure. In this example, the main event collapsing circuit 1230includes a flow restricting device 1232, such as an orifice or narrowpassage to slow energization (pressurization) of the collapsing circuitpassage 1270 and thereby delay activation of the main event collapse. Aswill be recognized, as an alternative to flow restricting device 1232, afluid passage of suitable length may be provided to implement a delay.The braking circuit 1240 may receive unrestricted flow from the solenoidvalve 1210. This configuration may be used to ensure that the brakingmechanism reaches steady state prior to main event collapse, therebypreventing opening of the intake valve(s) when cylinder pressures areexcessive. A check valve 1234 may be provided to facilitate backflow andunrestricted drain from the collapsing circuit 1234 back to the solenoidvalve 1210 during turn off of the braking mechanism. Re-activation ofthe main event motion may thus occur prior to deactivation (turn off) ofthe braking mechanism.

FIGS. 13, 14 15A and 15B illustrate an example system and apparatus forvalve event sequencing using a single-outlet proportional valve whichpermits a variable pressure supply to the braking and collapsingcircuits. As known in the art, a proportion valve provides varying levelof fluid output in proportion to the electrical current used to controlthe proportional valve. FIG. 13 is a schematic diagram of examplehydraulic components for implementing a braking circuit a main eventcollapsing circuit controlled by a proportional valve in an apparatusand system for sequencing valve events according to aspects of thedisclosure. Proportional valve 1310 feeds a collapsing circuit 1330 anda braking circuit 1340 via a single outlet. A check valve 1334implements a threshold minimum pressure required for activation of thecollapsing circuit 1330. When the proportional valve outlet pressure isincreased beyond this threshold, activation of the collapsing circuitoccurs, i.e., the check valve opens and permits fluid flow to thecollapsing circuit. FIG. 14 shows the system in a “brake off” mode inwhich the supply flow paths to the braking circuit 1340 and collapsingcircuit 1330 receive no flow, i.e., the proportional valve 1310 iscontrolled to provide no fluid output. In this and subsequent figures,the solid arrows represent active flow whereas the outlined arrowsrepresent non-active or no flow. FIG. 15A shows the system in a “brakeon” mode in which the proportional valve 1310 initially provides fluidto the circuits at a first pressure, lower than that needed to opencheck valve 1334. In this mode, the brake mechanism is activated underpressure in the braking circuit 1340. As pressure from the proportionalvalve increases (in proportion to increasing control current applied tothe proportional valve 1310) to a second pressure beyond the thresholdpressure set by check valve 1334, flow occurs in the collapsing circuit1330. In this manner, the sequential operation of the brake mechanismand the collapsing element can be controlled with appropriate control ofthe time rate of increase of pressure output by proportional valve 1310.A bleed path 1350 may permit flow of fluid from the collapsing circuitto ambient to enable quick response of the system to a “turn off”command (in which fluid output from the valve 1310 is discontinued) forthe braking mechanism. Bleed path 1350 provides for a rapid decrease inpressure in the collapsing circuit compared to the pressure decreasefrom a gradual backflow to the proportional valve. This provides for aquick deactivation of the collapsing circuit and ensures that the mainevent motion of exhaust valves will reactivate before the brakingcircuit “turns off.”

FIGS. 16A, 16B and 16C are schematic diagrams illustrating active andnon-active flows in an example apparatus and system which utilizes amultiple-outlet proportional valve. FIG. 16A illustrates the system in a“brake off” status, with non-active flows in both the braking circuit1640 and the collapsing circuit 1630, which may be supplied,respectively, by a first proportional valve outlet 1612 and a secondproportional valve outlet 1614. FIG. 16B illustrates the system in a“brake on” status with the first outlet 1612 providing flow to activatea braking circuit 1640. FIG. 16C illustrates a “brake on” status withthe second outlet 1614 providing flow to activate the collapsing circuit1630. Proportional valve 1610 may be configured such that it will onlysupply fluid to outlet one initially, and then, after a desired delayperiod has passed, will supply fluid to the second outlet. This may befacilitated by appropriate control signals to the proportional valve1610.

FIGS. 17A and 17B are cross-sections of an example engine brakingmechanism comprising a brake piston and hydraulic passages configured toindicate when the brake piston has fully indexed according to aspects ofthe disclosure. A braking mechanism piston 1710 may be mounted forsliding movement within a bore 1711 in a brake piston housing 1720, asdescribed above with reference to FIG. 3 . A fluid supply passage 1722formed in housing 1720 may be constantly pressurized and may terminateat a port 1724 communicating with the housing bore 1711. A main eventcollapsing or deactivation passage 1726 may also be formed in thehousing 1720 and may terminate at a port 1728 communicating with thehousing bore 1711. To facilitate selective communication of the supplypassage 1722 and the main event collapsing passage 1726, piston 1710 maybe provided with an annular channel or recess 1712. When piston is in adeactivated or non-steady state (i.e., transient) position, such as thatshown in FIG. 17A, channel or recess 1712 is disposed above (i.e., notaligned with) the deactivation passage port 1728 or the supply passageport 1724 and thus a collapsing circuit, fed by the collapsing passage1726 remains in a deactivated state (i.e., not collapsed). When piston1710 is in a steady-state position, shown in FIG. 17B, the channel orrecess 1712 is aligned with both ports 1724 and 1728 to provide forfluid communication between the supply passage 1722 and collapsingpassage 1728, thereby causing activation of the collapsing circuit.Thus, activation of the collapsing circuit occurs only after the brakepiston 1712 reaches a steady state position.

FIG. 18 illustrates a schematic representation of a system whichutilizes a spool valve operated under control of a solenoid valve tosequence activation of a braking circuit and a main eventcollapsing/deactivation circuit. A supply passage 1822 may be formed ina housing (rocker shaft) 1820 and may contain a supply of constantlypressurized fluid. An inlet 1812 of a solenoid valve 1810 may also befed from and communicate with supply passage 1822. Acollapsing/deactivation passage 1826 is also formed in the housing 1820.Solenoid valve outlet 1814 feeds a braking fluid passage 1830 alsoformed in the housing. Spool valve 1850, which is biased against thepressure in braking fluid passage 1830 by a spring 1852, may move withinthe housing 1820 under pressure in braking fluid passage 1830. When thebraking fluid passage 1830 is fully filled, spool valve 1850 moves to anindexed position where it provides for fluid communication between thesupply passage 1822 and collapsing passage 1826. Ports 1824 and 1828facilitate this fluid communication. Thus, the indexing of the spoolvalve 1850 provides sufficient delay to the activation of the collapsingcircuit.

As will be recognized, other implementations for creating delay betweenthe braking mechanism activation and lost motion device activation maybe utilized. For example, solenoids with different response times may beemployed for respective braking mechanism hydraulic circuit and the lostmotion hydraulic circuit. As a further example, mechanical components invalve trains may facilitate delay. Where the lost motion device andbraking mechanism include spring elements, for example, the spring forceconstants of the respective springs may be selected to facilitate adelay in the lost motion device activation and also facilitate morerapid response of the braking mechanism.

FIG. 19 illustrates example curves representing valve lift, valve trainforce and cylinder pressure as a function of time for prior art systems.As can be seen, prior art systems are characterized by load and cylinderpressure spikes that occur as a result of transient delays in brakevalve motion. These spikes typically subside after the system reachessteady state. However, the initial spike may result in excessive loadingon valve train elements as well as counter flow in intake flow paths.

FIG. 20 illustrates example curves representing valve lift, valve trainforce and cylinder pressure as a function of tie for an enhanced brakingsystem having one or more of the valve motion sequencing aspectsdescribed above. As can be seen, in the case where a delay isimplemented between activation of the braking mechanism and activationof the collapsing device (bridge solenoid activation), any transientintake loading is substantially equivalent to steady state loading ofthe system.

While particular preferred embodiments have been shown and described,those skilled in the art will appreciate that changes and modificationsmay be made without departing from the instant teachings. It istherefore contemplated that any and all modifications, variations orequivalents of the above-described teachings fall within the scope ofthe basic underlying principles disclosed above and claimed herein.

What is claimed is:
 1. A method for controlling counter flow andpressure in an intake flow path of an internal combustion engine duringan engine braking operation, the internal combustion engine comprisingat least one cylinder, an intake flow path communicating with the atleast one cylinder, at least one intake valve disposed in the intakeflow path, an exhaust flow path communicating with the at least onecylinder and at least one exhaust valve disposed in the exhaust flowpath, the method comprising: deactivating main event motion of the atleast one exhaust valve; initiating activation of an engine brakingmechanism associated with the at least one exhaust valve to perform a1.5 stroke or 2.0 stroke high power density braking operation, theinitiating step causing an initial transient state of the engine brakingmechanism, during which the engine braking mechanism is not yet capableof causing braking motion of the least one exhaust valve and duringwhich motion of the at least one intake valve tends to permitcounterflow from the at least one cylinder into the intake flow path,and thereafter a steady state of the engine braking mechanism, duringwhich the engine brake mechanism is ready to perform engine braking; andin response to the step of initiating activation of the engine brakingmechanism, and during the transient state of the engine brakingmechanism, initiating a step of counterflow management and therebymanaging counterflow in the intake flow path with at least one airflowmanagement device disposed in at least one of the intake flow path orthe exhaust flow path to thereby reduce counterflow that would otherwisebe permitted in the intake flow path during the transient state of theengine brake mechanism.
 2. The method of claim 1, wherein the airflowmanagement device includes an exhaust gas recirculation valve incommunication with the intake flow path and the exhaust flow path, theexhaust gas recirculation valve providing a first level of communicationbetween the intake flow path and the exhaust flow path duringsteady-state engine braking operation, and wherein managing counterflowin the intake flow path further comprises: no later than deactivation ofthe main event motion of the at least one exhaust valve, controlling theexhaust gas recirculation valve to increase communication between theintake flow path and the exhaust flow path above the first level ofcommunication.
 3. The method of claim 1, wherein the airflow managementdevice comprises an intake throttle valve disposed in the intake flowpath, the intake throttle providing a first level of flow in the intakeflow path during steady state engine braking operation, and whereinmanaging counterflow in the intake flow path further comprises: no laterthan deactivation of the main event motion of the at least one exhaustvalve, controlling the intake throttle valve to restrict flow in theintake flow path below the first level of flow.
 4. The method of claim1, wherein the airflow management device comprises a turbocharger incommunication with the intake flow path and the exhaust flow path, aturbine of the turbocharger configured to provide a first level of boostpressure in the intake flow path during steady state engine brakingoperation, and wherein managing counterflow in the intake flow pathfurther comprises: no later than deactivation of the main event motionof the at least one exhaust valve, controlling the turbine to decreaseboost pressure in the intake flow path below the first level of boostpressure.
 5. The method of claim 1, wherein the airflow managementdevice comprises a turbocharger in communication with the intake flowpath and the exhaust flow path and a wastegate in communication with theexhaust flow path, the wastegate and the turbocharger configured toprovide a first level of boost pressure in the intake flow path duringsteady state engine braking operation, and wherein managing counterflowin the intake flow path further comprises: no later than deactivation ofthe main event motion of the at least one exhaust valve, controlling thewastegate to decrease boost pressure provided by the turbocharger in theintake flow path below the first level of boost pressure.
 6. The methodof claim 1, wherein the airflow management device comprises aturbocharger in communication with the intake flow path and the exhaustflow path and an exhaust throttle valve in the exhaust flow path, theexhaust throttle valve and the turbocharger configured to provide afirst level of boost pressure in the intake flow path during steadystate engine braking operation, and wherein managing counterflow in theintake flow path further comprises: no later than deactivation of themain event motion of the at least one exhaust valve, controlling theexhaust throttle valve to decrease boost pressure provided by theturbocharger in the intake flow path below the first level of boostpressure.
 7. The method of claim 1, wherein the airflow managementdevice comprises a turbocharger in communication with the intake flowpath and the exhaust flow path and a compressor bypass valve incommunication with the intake flow path, the compressor bypass valve andthe turbocharger configured to provide a first level of boost pressurein the intake flow path during steady state engine braking operation,and wherein managing counterflow in the intake flow path furthercomprises: no later than deactivation of the main event motion of the atleast one exhaust valve, controlling the compressor bypass valve todecrease boost pressure provided by the turbocharger in the intake flowpath below the first level of boost pressure.
 8. The method of claim 1,wherein the airflow management device comprises a passive blow-off valvein communication with the intake flow path, and wherein managingcounterflow in the intake flow path further comprises: configuring thepassive blow-off valve to open when pressure within in the intake flowpath exceeds a predetermined threshold.
 9. The method of claim 1,wherein the airflow management device comprises an active blow-off valvein communication with the intake flow path, and wherein managingcounterflow in the intake flow path further comprises: no later thandeactivation of the main event motion of the at least one exhaust valve,controlling the active blow-off valve to open.
 10. The method of claim1, wherein the step of deactivating the main event motion of the atleast one exhaust valve further comprises collapsing an exhaustvalvetrain lost-motion device to absorb main event motion of the atleast one exhaust valve.
 11. The method of claim 10, further comprisingthe step of deactivating main event motion of the at least one intakevalve and adding a secondary motion to at least one of the at least oneexhaust valve and the at least one intake valve.
 12. The method of claim1, further comprising the step of deactivating main event motion of theat least one intake valve and adding a secondary motion to at least oneof the at least one exhaust valve and the at least one intake valve. 13.The method of claim 1, further comprising the step of adding a secondarymotion to the at least one exhaust valve when the main event motion ofthe at least one exhaust valve is deactivated.
 14. The method of claim1, further comprising the step of maintaining main event motion of theat least one intake valve while the main event motion of the at leastone exhaust valve is deactivated.
 15. The method of claim 1, wherein thebraking motion of the at least one exhaust valve includes two respectivesecondary lift events of the at least one exhaust valve, the twosecondary lift events corresponding to immediately successive strokes ofa piston in a four-stroke engine cycle.
 16. The method of claim 1,wherein deactivating main event motion of the at least one exhaust valvecomprises activating a lost motion device.
 17. The method of claim 16,further comprising delaying activation of the lost motion device untilthe engine brake mechanism is in the steady state.